As I understand, matter devices can communicate via two options: wifi, or a "thread" network. The thread network was developed as part of the matter ecosystem, I believe, and requires a thread border router in order to complete the system. If a particular matter device connects via wifi, then I expect you would be able to add this device to your ISY, though there may not be full functionality. If a particular matter device communicates via the thread network, then I expect that you will have little success trying to add the device to your ISY.